A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. The fan section and compressor section together are typically referred to as the cold section. The combustor section and turbine section together are typically referred to as the hot section. Bladed disk turbomachinery of the cold section and the turbine section rotate at great speed which places the blades under severe stress. For operational analysis and safety it is desirable to monitor these stresses. Non-Intrusive Stress Measurement System (NSMS) are systems which monitor these stresses without relying on sensors integral to or intruding on the rotating turbomachinery. NSMS sensors mounted external to the blade disk are used to measure each blade's behavior including vibratory response characteristics such as stress, phase, frequency, resonance, and damping.
Un-lensed fiber optic probes may receive reliable signals when held in close proximity to the blade. Typical standoff distances are less than 10 mm from the blade, thus probe holders are used to keep the probe in proximity to the blade at the correct standoff. The current NSMS un-lensed probe holders have a probe housing with a seating step and a viewing aperture. The optical fibers may be sheathed by a thin walled hypo tube which provides protection from mechanical damage and a pathway for coolant to flow around the fibers.
During assembly, the probe is unsecured after insertion into the probe holder and may back away from the seating step during a welding operation, thus fixing the probe at an improper standoff distance. In addition, spot welding the strap directly to the thin wall hypo tube may compromise the hypo tube's ability to contain the coolant flow. Weld current, at times, may be lowered to insure hypo tube integrity but may also compromise the weld penetration.